I cannot see how anyone could allow a trial to be conducted with no witnesses, particularly when the defendant has repeatedly refused to produce witnesses and documents himself. A trial is intended to bring out the truth. What are these senators thinking? What do they want to accomplish by making a sham of the proceedings? This goes beyond any identification with a political party. It is a matter of basic principle. And each senator is supposed to sit as an impartial juror, not come into the chamber with his/her mind made up already and refuse to listen to evidence.
If witnesses were permitted, the defendant could call his own, and cross-examine those called by the prosecution.
That our senators have become this openly corrupt is truly frightening. They are proving that they have no allegiance to, or love for the U.S.A. In the mean time, a vote against witnesses will lead to a legal finding of not proven guilty, but it will not result in an exoneration, given the dubious circumstances in which it was arrived at.